I'm new here and i would be very grateful if anyone could help me. I have an old but very good amplifier with a broken volume control. It is a log pot 100k dual channel. What a confusing me is each channel has a 4th pin which appears to be connected to the board with the tone controls. It is an Alps pot but i can not find a similar one anywhere. Each channel has pin 1 ground, 2 wiper, 3 signal in, 4 50% tap. As i can not find any pot with this 4th pin is this essential to the operation of the amplifier? Any help would be very much appreciated. Many thanks in anticipation.

I'm new here and i would be very grateful if anyone could help me. I have an old but very good amplifier with a broken volume control. It is a log pot 100k dual channel. What a confusing me is each channel has a 4th pin which appears to be connected to the board with the tone controls. It is an Alps pot but i can not find a similar one anywhere. Each channel has pin 1 ground, 2 wiper, 3 signal in, 4 50% tap. As i can not find any pot with this 4th pin is this essential to the operation of the amplifier? Any help would be very much appreciated. Many thanks in anticipation.

The tap is used to boost the treble when the control is turned low. (usually)
You can hook up a 3 terminal pot but loose treble at very low volumes.To help this, put a capacitor between the input and the wiper.
could be 50 pf, 100 pf, 150 pf or even more depending on your personal listening taste.